Interleukin 6 (IL-6) is a potent pleiotropic cytokine that regulates cell growth and differentiation and is also an important mediator of acute inflammatory responses. IL-6 exhibits its action via a receptor complex consisting of a specific IL-6 receptor (IL-6R) and a signal transducing subunit (gp130). Dysregulated IL-6 signaling has been implicated in the pathogenesis of many diseases, such as multiple myeloma, autoimmune diseases and prostate cancer. Accordingly, there exists a need for therapies that neutralize the biological activities of IL-6 and/or IL-6R.